1. Field of the Invention
The present invention relates to an optical fiber joint type ion-concentration measurement apparatus in which electrical signals which are detected by an ion selective electrode are transformed into optical signals which are transmitted to a receiving side of the apparatus by means of optical fibers.
2. Description of the Prior Art
An optical fiber joint type ion-concentration measurement apparatus of this kind has an advantage in that measurement errors due to disturbances and ground loop voltages can be significantly reduced in comparison to that of apparatus in which the transmitting side is connected to the receiving side by electrical cables.
However, in the conventional optical fiber joint type ion-concentration measurement apparatus, since the signals detected by an ion electrode are either amplified and used as is or the amplified signals are modulated in frequency through a voltage/frequency converter and used to cause an LED (Light Emitting Diode) to emit light, an extremely large electrical power consumption is needed and many problems must be solved in order to use them practically. That is to say, since a large consumption of electrical power is required, it is necessary to use a large-sized battery at the transmitting side or to connect the transmitting side to the receiving side by means of a power supply cable. In the former method, since the transmitting side apparatus becomes large-sized and heavy, it is difficult to carry about. In the latter method, it is not worthwhile to use an optical fiber joint type ion-concentration measurement apparatus since the advantages thereof are lost by the use of the power supply cable. At present, the apparatus, which use liquid crystal devices having a low power consumption instead of the LED devices are being proposed. However, since liquid crystal devices do not emit light by themselves but merely change the transmission of light, it is necessary to transmit the light to be irradiated to the liquid crystal devices from the receiving side, whereby the apparatus using such liquid crystal devices have disadvantages in that one more optical fiber is required and the circuit of the transmitting side is complicated in construction.